Annual report pursuant to Section 13 and 15(d)

Stockholders' equity - Stock-Based Compensation (Details)

v3.20.4
Stockholders' equity - Stock-Based Compensation (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Options granted, exercise price range, lower limit (usd per share) $ 0.71  
Options granted, exercise price range, upper limit (usd per share) $ 0.78  
Historical forfeiture rate (percent) 15.00%  
Tecogen    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Options granted 1,440,000 88,500
Options granted, exercise price range, lower limit (usd per share) $ 0.71 $ 3.40
Options granted, exercise price range, upper limit (usd per share) $ 0.78 $ 3.80
Award vesting period 4 years  
Award expiration period 10 years  
Fair value of options issued $ 404,460 $ 89,772
Weighted-average grant date fair value of options granted $ 0.28 $ 1.01
Exercised (shares) 1,000 24,515
Exercised, aggregate intrinsic value $ 20 $ 19,794
Recognized stock-based compensation 190,944 163,464
Compensation cost related to unvested restricted stock awards and stock option awards not yet recognized $ 523,989 $ 340,503
Compensation cost not yet recognized, weighted average period of recognition 2 years 1 month 6 days  
Tecogen | Amended Plan | Stock Options    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Shares of common stock reserved for future issuance 3,838,750  
Number of shares remaining available for future issuance 761,812 1,906,180
Remaining Options | Tecogen | Stock Options    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Award vesting period   4 years
Award expiration period   10 years